Page 1 : 10. S-BLOCK ELEMENTS, HAIZEL G. ROY, H.S.S.T. (HG) CHEMISTRY, GOVT. H.S.S. KALAMASSERY, ERNAKULAM

Page 2 : In, , s-block elements the last electron enters the outermost, , s-orbital., It includes elements of group 1 and 2 and He in group 18., It consists of six elements Li, Na, K, Rb, Cs and Fr., These, , are called alkali metals because they react with, , water to form soluble hydroxides which are strong bases or, alkalies.

Page 3 : The group 2 includes Be, Mg, Ca, Sr, Ba and Ra., These, , elements with the exception of Be are commonly, , known as alkaline earth metals., They, , are so called because their oxides are found in the, , earth’s crust., The, , general outer electronic configuration of s-block, , elements is ns1 or ns2 .

Page 4 : DIAGONAL RELATIONSHIP, The, , similarity in properties shown by diagonally placed, , elements of second and third periods in modern, periodic table is called diagonal relationship., Li shows similarities to Mg., Be shows similarities Al.

Page 5 : CAUSE OF DIAGONAL RELATIONSHIP, As, , we move from left to right across a period, the electronegativity, , increases., But it decreases when we move from top to bottom., As, , a result of these two opposite changes, as we move diagonally,, , these two effects tend to cancel each other and there is no marked, change in electronegativity., Because, , of the similar values of electronegativities, the diagonal, , elements have similar chemical properties.

Page 6 : ANOMALOUS BEHAVIOUR OF THE FIRST MEMBER OF A GROUP, The, , first member in each group shows certain properties which are, , different from that of the other elements in their respective groups., This anomalous behaviour of the first member in each group is due to, The very small size of the atoms, High Ionisation energies, High electronegativities, Absence of vacant d orbitals.

Page 7 : GROUP I ELEMENTS, ALKALI METALS

Page 8 : ATOMIC AND PHYSICAL PROPERTIES, ELECTRONIC CONFIGURATION, , The general electronic configuration of alkali metals, may be represented as [Noble gas] ns1 .

Page 9 : ATOMIC AND IONIC RADII, The alkali metals have the largest sizes in a particular period, , of the periodic table., With, , the increase in atomic number, the atom becomes, , larger., The monovalent ions (M+) are smaller than the parent atom., The, , atomic and ionic radii of alkali metals increase on, , moving down the group.

Page 10 : IONISATION ENERGY, The alkali metals have low ionisation energies., Their atomic sizes are quite large and the valence electrons are, , quite loosely held by the nucleus., On moving down the group, the ionisation energy decreases., It is due to the increase in size of the atoms., Increase, , in the magnitude of screening effect caused by the, , increase in the number of intervening electrons.

Page 11 : HYDRATION ENTHALPY, The, , hydration enthalpies of alkali metal ions decrease, , with increase in ionic sizes., The smaller the ion, the more is the extent of hydration., Due, , to this, in aqueous solution, the hydration enthalpy, , decreases in the order Li+ > Na+ > K+ > Rb+ > Cs+

Page 12 : PHYSICAL PROPERTIES

Page 13 : 1. METALLIC CHARACTER, All, , the alkali metals are silvery white, soft and light, , metals., The metallic character increases down the group., 2. DENSITY, Because of the large size, alkali metals have low density., The Density generally increases down the group.

Page 14 : MELTING AND BOILING POINTS, The melting and boiling points of alkali metals are low., It, , indicates weak metallic bonding due to the presence of, , only a single valence electron in them., The, , melting and boiling points decreases down the, , group.

Page 15 : When alkali metals or their salts are heated in the flame of a Bunsen, , burner, they impart characteristic colours to the flame.

Page 16 : Alkali metals have low Ionisation energy., Therefore,, , the electrons present in their atoms get readily, , excited to higher energy states by absorbing energy from the, visible region of the light., When, , these electrons jump back to their ground state, they, , emit energy in the form of radiations., These, , radiations fall in the visible region, imparting, , characteristic colouration to the flame.

Page 17 : CHEMICAL PROPERTIES

Page 18 : REACTIVITY TOWARDS AIR, Alkali metals tarnish in dry air., It is due to the formation of their oxides., These oxides in turn react with moisture to form, , hydroxides., They burn vigorously in oxygen forming oxides.

Page 19 : When heated in excess of air, Li forms normal oxide., Sodium forms peroxides., K, Rb and Cs forms superoxide.

Page 20 : REACTIVITY TOWARDS WATER, The alkalie metals react with water to form hydroxide, and dihydrogen.

Page 21 : REACTIVITY TOWARDS DIHYDROGEN,  On, , heating, alkali metals react with hydrogen to form hydrides of the, , formula, MH.,  All the alkali metal hydrides are ionic solids with high melting points., ,  The hydrides are strong reducing agents.,  It reduce water with the liberation of hydrogen.

Page 22 : REACTIVITY TOWARDS HALOGENS, Alkali metals react with halogens to form halides of the, general formula, MX.

Page 23 : REDUCING NATURE, The alkali metals are strong reducing agents., Lithium, being the most and sodium, the least powerful., The, , reducing character increases down the group from, , Na to Cs because of the decrease in ionisation energy.

Page 24 : SOLUBILITY IN LIQUID AMMONIA, The, , alkali metals dissolve in liquid ammonia giving deep blue, , solutions which are conducting in nature., The, , blue colour of the solution is due to the ammoniated electrons, , (solvated electrons)., Ammoniated electrons absorbs energy in the visible region of light., This imparts blue colour to the solution., The solutions are paramagnetic.

Page 25 : SALTS OF OXO ACIDS, Since, , alkali metals are strongly electropositive, they, , form salts with oxo acids., Oxo, , acids are those in which the acidic proton is on a, , hydroxyl group with an oxo group attached to the same, atom.

Page 27 : ANOMALOUS PROPERTIES OF LITHIUM, Lithium is much harder., The, , melting point and boiling point are higher than the, , other alkali metals., Lithium, , is the least reactive but the strongest reducing, , agent among all the alkali metals.

Page 28 : Lithium reacts with nitrogen to form a nitride, Li, , 3, , N., , LiCl is deliquescent and crystallizes as a hydrate, LiCl. 2H, , 2, , O., , LiOH is a weak base., Lithium does not form acetylide on reaction with acetylene.

Page 29 : DIAGONAL SIMILARITIES BETWEEN Li and Mg, Both, , Li and Mg are harder than other elements in the, , respective groups., Both, , Li and Mg form a nitride by direct combination with, , nitrogen, Both, , Li and Mg react with oxygen to form normal oxides, , Li2O and MgO respectively.

Page 30 : The, , hydroxides of Li and Mg are weak bases and they, , decompose on heating., Carbonates, , of Li and Mg decompose easily on heating to, , form the oxide and CO2 ., Both LiCl and MgCl, Both, , 2, , are soluble in ethanol., , LiCl and MgCl2 are deliquescent and crystallizes as, , hydrates LiCl.2H2O and MgCl2 .8H2O.

Page 31 : SOME IMPORTANT, COMPOUNDS OF SODIUM

Page 32 : Sodium, , forms many industrially important compounds, , like, sodium carbonate (Na, , 2, , CO3), , sodium chloride (NaCl), sodium hydroxide (NaOH), sodium hydrogen carbonate (NaHCO, , 3, , )

Page 33 : SODIUM CARBONATE (Na2CO3), Sodium carbonate is also known as washing soda or soda, ash.

Page 34 : PREPARATION, Sodium carbonate is generally prepared by Solvay process., Prepared, , by passing CO2 gas under pressure into a strong sodium, , chloride solution saturated with ammonia., Sodium Hydrogen Carbonate is precipitated.

Page 35 : Sodium hydrogen carbonate on heating gives sodium carbonate., , In this process, NH, , 3, , is recovered when the solution containing NH4Cl, , is treated with Ca(OH)2 ., Calcium chloride is obtained as a by-product.

Page 36 : K2CO3CANNOT BE PREPARED BY SOLVAY PROCESS, Potassium, , carbonate cannot be prepared by Solvay, , process., This is because the solubility of KHCO, Hence, , tower., , 3, , is fairly large., , it does not precipitate easily in the carbonation

Page 37 : PROPERTIES, Sodium carbonate is a white crystalline solid., It exists as a decahydrate, Na, , 2, , CO3 .10H2O., , This is also called washing soda., It is readily soluble in water., On, , heating, the Decahydrate loses its water of crystallization, , to form monohydrate.

Page 38 : Above, , 373K,, , the, , monohydrate, , becomes, , completely, , anhydrous and changes to a white powder called soda ash., , The solution of Na, , 2, , CO3 is alkaline due to hydrolysis.

Page 39 : USES, Sodium Carbonate is used, in water softening, laundering and cleaning., in the manufacture of glass, soap, borax and caustic soda., in paper, paints and textile industries., It, , is an important laboratory reagent both in qualitative and, , quantitative analysis.

Page 40 : SODIUM CHLORIDE (NaCl), The most abundant source of sodium chloride is sea water., Sea water contains 2.7 to 2.9 % by mass of the salt.

Page 41 : PREPARATION, In India, common salt is generally obtained by the evaporation of sea, , water., Crude NaCl is generally obtained by crystallization of brine solution., It, , contains sodium sulphate, calcium sulphate, calcium chloride and, , magnesium chloride as impurities., To, , obtain pure sodium chloride, the crude salt is dissolved in, , minimum amount of water.

Page 42 : The insoluble impurities are filtered., The, , solution is then saturated with hydrogen chloride, , gas., Crystals of pure sodium chloride separate out., Calcium, , and magnesium chloride being more soluble, , than sodium chloride, remain in solution.

Page 43 : PROPERTIES, Sodium chloride melts at 1082K., It has a solubility of 36g in 100g of water at 273K., The, , solubility does not increase appreciably with increase, , in temperature.

Page 44 : USES, It, , is used as common salt or table salt for domestic, , purpose., It is used for the preparation of Na, , 2, , O2 , NaOH and Na2CO3 .

Page 45 : SODIUM HYDROXIDE (NaOH), Sodium hydroxide is also known as caustic soda.

Page 46 : PREPARATION, Sodium, , hydroxide is prepared commercially by the electrolysis of, , sodium chloride in Castner-Kellner cell., Sodium hydroxide is obtained by the electrolysis of brine solution., Cathode is made up of mercury and anode is made up of carbon., Sodium metal is discharged at the cathode., It combines with mercury to form sodium amalgam., Chlorine gas is evolved at the anode.

Page 47 : The amalgam is treated with water to give sodium hydroxide, and hydrogen gas.

Page 49 : PROPERTIES, Sodium hydroxide is a white, translucent solid., It melts at 591K., It is readily soluble in water to give a strong alkaline solution., Crystals of sodium hydroxide are deliquescent., The, , sodium hydroxide solution at the surface reacts with the, , CO2 in the atmosphere to form Na2CO3 .

Page 50 : USES,  Sodium hydroxide is used: in the manufacture of paper, soaps, artificial silk etc.,  for the purification of bauxite.,  as an important laboratory reagent.,  in petroleum refining.,  for mercerizing cotton fibres.,  for refining vegetable oils.,  for preparing various sodium salts like sodium chlorate, hypochlorite, , etc.

Page 51 : SODIUM HYDROGEN CARBONATE, Sodium Hydrogen Carbonate is known as baking soda., It, , is called so because it decomposes on heating to generate bubbles, , of CO2 .

Page 52 : PREPARATION, It, , is prepared by saturating a solution of sodium carbonate, , with carbon dioxide., The, , white crystalline powder of sodium hydrogen carbonate,, , being less soluble, gets separated out.

Page 53 : USES, NaHCO, , 3, , is used, , as a laboratory reagent., in baking powder., in fire extinguishers., as, , a mild antiseptic for skin, , infections.

Page 54 : BIOLOGICAL IMPORTANCE OF SODIUM, Sodium ions are found outside the cells., It, , is located in blood plasma and in the interstitial fluid which, , surrounds the cells., These ions participate in the transmission of nerve signals., Regulates the flow of water across cell membranes, Helps in the transport of sugars and amino acids into cells.

Page 55 : BIOLOGICAL IMPORTANCE OF POTASSIUM, Potassium, , ions are the most abundant cations within cell, , fluids., They activate many enzymes., Participate in the oxidation of glucose to produce ATP., With, , sodium it is responsible for the transmission of nerve, , signals.

Page 56 : GROUP II ELEMENTS, ALKALINE METALS

Page 57 : Group, , 2 of the periodic table consists of the elements Be, Mg,, , Ca, Sr, Ba and Ra., These, , elements except beryllium are known as alkaline earth, , metals., Radium, the last member of the group is radioactive in nature., Beryllium shows diagonal relationship to Aluminium.

Page 58 : ATOMIC AND, PHYSICAL PROPERTIES

Page 59 : ELECTRONIC CONFIGURATION, The, , general electronic configuration may be, , represented as [Noble gas] ns2, where n = 2 to 7.

Page 60 : ATOMIC RADII, The, , atomic and ionic radii of the alkaline earth metals are, , smaller than those of the corresponding alkali metals in the, same periods., This is due to the increased nuclear charge in these elements.

Page 61 : IONISATION ENERGIES, The, , alkaline earth metals have low ionisation energies due to, , fairly large size of the atoms., The, , first ionisation energies of the alkaline earth metals are, , higher than those of the corresponding group I metals., This, , is due to their small size as compared to the, , corresponding alkali metals.

Page 62 : HYDRATION ENTHALPIES, The hydration enthalpies of alkaline earth metal, , ions decrease, , with increase in ionic size down the group., Be2+ > Mg2+ > Ca2+ > Sr2+ > Ba2+, The, , hydration enthalpies of alkaline earth metal ions are, , larger than those of alkali metal ions., Compounds, , of alkaline earth metals are more extensively, , hydrated than those of alkali metals.

Page 63 : PHYSICAL, PROPERTIES

Page 64 : METALLIC CHARACTER, The alkaline earth meals are silvery white, lustrous and, , relatively soft, but harder than the alkali metals., Be and Mg appears to be somewhat greyish.

Page 65 : DENSITY, The, , alkaline earth metals are denser and harder than the, , alkali metals of the corresponding periods., It, , is because of the smaller size and stronger metallic bonds, , resulting in more closely packed crystal lattices.

Page 66 : MELTING AND BOILING POINTS, Alkaline earth metals have higher melting and boiling points., This, , is because of their smaller size and more closely packed, , structures.

Page 67 : ELECTROPOSITIVE CHARACTER, Alkaline earth metals are electropositive in nature., Due, , to, , higher, , ionisation, , energies,, , these, , are, , less, , electropositive than alkali metals., Within the group, the electropositive character increases from, , Be to Ba.

Page 68 : FLAME COLOURATION, Ca,, , Sr and Ba impart characteristic brick red, crimson red and, , apple green colours to the flame respectively., Be, , and Mg does not impart any colour to the flame due to, , small size and high ionisation energies., The, , excitation of electrons is not possible by the energy, , available from the flame.

Page 69 : CHEMICAL, PROPERTIES

Page 70 : REACTIVITY TOWARDS AIR,  Be, , and Mg are kinetically inert to oxygen and water because of the, , formation of an oxide film on their surface.,  Powdered Be burns brilliantly on ignition in air to give BeO and Be,  Mg, , N2 ., , 3, , is more electropositive and burns with dazzling brilliance in air to give, , MgO and Mg3N2 .,  Ca, Sr and Ba are readily attacked by air to form the oxide and nitride.,  They, , also react with water with increasing vigour even in cold to form, , hydroxides.

Page 71 : REACTIVITY TOWARDS HYDROGEN, All, , the elements except Be combine with hydrogen upon, , heating to form their hydrides, MH2., , BeH, , 2, , can be prepared by the reaction of BeCl2 with LiAlH4.

Page 72 : REACTIVITY TOWARDS ACIDS, The alkaline earth metals readily react with acids liberating, dihydrogen.

Page 73 : REACTIVITY TOWARDS HALOGENS, All, , the alkaline earth metals combine with halogen at, , elevated temperatures forming their halides., BeCl, , 2, , is formed by passing chlorine over a heated mixture of, , Beryllium oxide and carbon.

Page 74 : STRUCTURE OF BeCl2, In the solid state, BeCl, , 2, , exists as a polymer., , Each Be atom is surrounded by four chlorine atoms., Two, , of the chlorine atoms are bonded by covalent bonds and, , the remaining two by coordinate bonds.

Page 75 : REDUCING NATURE, Alkaline earth metals are strong reducing agents., They have large negative values of their reduction potentials., Their, , reducing power is less than those of their corresponding, , alkali metals.

Page 76 : SOLUTIONS IN LIQUID AMMONIA, Alkaline earth metals dissolve in liquid ammonia to give deep, blue black coloured solutions forming ammoniated ions.

Page 77 : FORMATION OF OXIDES, Alkaline, , earth metals react with air or oxygen slowly upon, , heating to form oxides., Be, Mg and Ca forms monoxides., Sr and Ba forms peroxides.

Page 78 : FORMATION OF HYDROXIDES, Elements of group 2 have lesser tendency to react with water., On, , heating, they react with water to form hydroxide and, , liberate hydrogen., The, , hydroxides are basic in nature, except Be(OH)2 which is, , amphoteric., The basic strength increases down the group., It is due to the decrease in the ionisation energies.

Page 79 : ANOMALOUS BEHAVIOUR OF BERYLLIUM, The properties of Be differs from those of the other elements, , of the group., It is because of, Its small size, Relatively high ionisation energy, Relatively high electronegativity, Absence of vacant d orbitals in the valence shell.

Page 80 : DIFFERENCES, Be compounds are more covalent in nature., Be does not react with water even at high temperatures., BeO is amphoteric., Be does not react with H, , 2, , Be, , 2, , to give hydride., , C reacts with water to give methane.

Page 81 : DIAGONAL RELATIONSHIP BETWEEN Be and Al, Both Be and Al have same electronegativity., Both Be and Al form covalent compounds., Both Be and Al are resistant to the action of acids., The hydroxides of Be and Al are amphoteric., Chlorides, , of both Be and Al have bridged structures in vapour, , phase., Carbides, , methane., , of both Be and Al undergo hydrolysis to give

Page 82 : SOME IMPORTANT COMPOUNDS, OF CALCIUM

Page 83 : COMPOUNDS OF CALCIUM, Important compounds of calcium are, Calcium oxide, Calcium hydroxide, Calcium sulphate, Calcium carbonate, Cement

Page 84 : CALCIUM OXIDE OR QUICK LIME (CaO)

Page 85 : PREPARATION, It, , is prepared on a commercial scale by heating limestone in a, , rotary kiln at 1070-1270K., , The, , CO2 is removed as soon as it is produced to enable the, , reaction to proceed to completion.

Page 86 : PROPERTIES, Calcium oxide is a white amorphous solid., It has a melting point of 2870K., On, , exposure to atmosphere, it absorbs moisture and carbon, , dioxide., The, , addition of limited amount of water breaks the lump of, , lime., This process is called slaking of lime.

Page 87 : USES, Calcium Oxide is used, as a building material, in softening of hard water., in the manufacture of calcium carbide., as a drying agent., in the purification of sugar.

Page 88 : CALCIUM HYDROXIDE OR SLAKED LIME Ca(OH)2

Page 89 : PREPARATION, Calcium hydroxide is prepared by adding water to quick lime,, CaO.

Page 90 : PROPERTIES, Calcium hydroxide is a white amorphous powder., It is sparingly soluble in water., A suspension of slaked lime in water is called milk of lime., The filtered solution is called lime water.

Page 91 : When, , CO2 is passed through lime water, it turns milky due to, , the formation of CaCO3 ., On, , passing excess of CO2 , the precipitate dissolves to form, , calcium hydrogen Carbonate., Milk, , of lime reacts with chlorine to form hypochlorite, a, , constituent of bleaching powder.

Page 92 : USES, Calcium Hydroxide is used, in the production of mortar, a building material., as lime water in laboratories., for the manufacture of bleaching powder., Milk of lime is used for white washing.

Page 93 : CALCIUM CARBONATE (CaCO3), It occurs in nature in several forms like limestone, chalk,, marble etc.

Page 94 : PREPARATION, Prepared by passing carbon dioxide through slaked lime or by, the addition of Na2CO3 to CaCl2 .

Page 95 : PROPERTIES, Calcium carbonate is a white fluffy powder., It is almost insoluble in water., When heated to 1200K, it decomposes to evolve carbon, , dioxide., It reacts with dilute acids to liberate carbon dioxide.

Page 96 : USES, Calcium Carbonate is used, as a building material in the form of marble., for the manufacture of quick lime., Calcium carbonate along with MgCO, Specially precipitated CaCO, , 3, , 3, , is used as a flux in metallurgy., , is extensively used in the manufacture of, , high quality paper., as, , an antacid, mild abrasive in tooth paste, a constituent of chewing, , gum and filler in cosmetics.

Page 98 : PREPARATION, Plaster of Paris is obtained by heating gypsum to 393 K., , Above, , 393 K, no water of crystallization is left and anhydrous, , calcium sulphate, CaSO4 is formed., This is known as dead burnt plaster.

Page 99 : When, , plaster of Paris is mixed with water, it forms a paste, , which sets to a hard mass in 5 to 15 min., This is called setting of Plaster of Paris., During setting, it takes up water and forms CasO, , 4, , .2H2O.

Page 100 : USES, Calcium Sulphate is used, for setting broken and fractured bones., for making statues, models, decorative materials etc., for producing moulds for Industries like pottery and ceramics., in dentistry and in ornamental work.

Page 101 : CEMENT, Cement, , is an important building, , material., It, , was first introduced in England in, , 1824 by Joseph Aspidin., It is also called Portland cement., It, , resembles the natural lime stone, , quarried in the Isle of Portland,, England.

Page 102 : WHAT IS CEMENT ?, Cement, , is essentially a finely ground mixture of calcium and, , aluminium silicates along with small quantities of gypsum, which sets to a hard mass when reacted with water., Cement, , is a product obtained by combining a material, rich in, , lime, CaO with other material such as clay which contains, silica, SiO2 along with the oxides of aluminium, Iron and, Magnesium.

Page 103 : MANUFACTURE OF CEMENT, The, , raw materials for the manufacture of cement are limestone and, , clay., When clay and lime are strongly heated together, they fuse and react, , to form cement clinker., This clinker is mixed with 2-3% by weight of gypsum to form cement., Thus, , important ingredients present in Portland cement are, , dicalcium silicate (Ca2SiO4) 26%, tricalcium silicate (Ca3SiO5 ) 51%, and tricalcium aluminate (Ca3Al2O6 ) 11%.

Page 104 : SETTING OF CEMENT, When, , cement is mixed with water it reacts to form a gelatinous mass, , which sets to a hard mass., The, , transition of cement from the gelatinous mass to a hard mass is, , called setting of cement., During setting, three dimensional cross links are formed between, ----Si―O―Si----, , and ----Si―O―Al---- chains making the material quite, , hard., The, , purpose of adding gypsum is to slow down the process of setting, , of the cement so that it gets sufficiently hardened.

Page 105 : USES OF CEMENT, Cement is used, in concrete and reinforced concrete., in, , plastering and in construction of, , bridges, dams and buildings.

Page 106 : BIOLOGICAL IMPORTANCE OF Mg & Ca, An adult body contains about 25g of Mg, 1200g of Ca, 5g of Iron, , and 0.06g of copper., The, , daily requirement in the human body has been estimated, , to be 200-300mg., All, , enzymes that utilize ATP in phosphate transfer require, , magnesium as the cofactor.

Page 107 : The main pigment for the absorption of light in plants is, chlorophyll which contains Mg., About 99% of Ca is present in bones and teeth., It also plays important roles in neuromuscular function,, Interneuronal transmission, blood coagulation etc.